Sender in signal-to-signal connection

Question

There is a function QObject::sender(), than, when invoked in a slot, provides the QObject* pointer to the sending object.

It's behaviour is far less useful if you have the following structure.

class A : public QObject { Q_OBJECT 
    ...
    signals: 
        void foo(); 
};

class B : public QObject { Q_OBJECT 
    ...
    signals: 
        void foo(); 
};

class C : public QObject { Q_OBJECT
    ... 
    public slots: 
        void bar() { qDebug() << sender(); }  
};

A a; 
B b;
C c;


connect(&A, SIGNAL(foo()), &B, SIGNAL(foo()));
connect(&B, SIGNAL(foo()), &C, SLOT(bar()));

A::whatever() { emit foo(); } 

C::bar() indicates B as the emitter. How can I get the original emitting object, without dealing with all the relays?

Unfortunately QObject::sender() is protected so this naive approach in C::bar() wouldn't compile (not sure if it ever could work, but that's my only idea to traverse the sender() backwards):

QObject *ptr = this;
while ((ptr = ptr->sender()) != NULL)
    qDebug() << ptr->objectName();

---

To answer some of the questions raised in comments:

• A - custom widget (lots of dynamically created ones) (holding some data, pointers, whatnot)
• B - custom top-level UI element (member of the QStackedWidget, handles some UI responsibilities)
• C - (in practice, C1, C2, C3) - work that needs to be performed (using common state, such as DSP queue) on data stored in As.

Ultimately, A needs to know very little about Cs (or even if anything cares about it's signals). B is where the UI aggregation takes place (also the top-level UI calls Cs to set DSP parameters etc). Cs need to know if sender() is qobject_cast'able to IA interface.

It can be reworked to something along the lines of:

class A : public QObject { Q_OBJECT 
    ...
    signals: 
        void foo(QObject*); 
};

class B : public QObject { Q_OBJECT 
    ...
    signals: 
        void foo(QObject*); 
};

class C : public QObject { Q_OBJECT
    ... 
    public slots: 
        void bar(QObject* mySender) { qDebug() << mySender; }  
};

A a; 
B b;
C c;


connect(&A, SIGNAL(foo(QObject*)), &B, SIGNAL(foo(QObject*)));
connect(&B, SIGNAL(foo(QObject*)), &C, SLOT(bar(QObject*)));

A::whatever() { emit foo(this); }